1. Technical Field
Several aspects of the present invention relate to a photoresist film placing method, a semiconductor device manufacturing method, an electro-optical device, and an electronic device.
2. Related Art
The photosensitive material used to form a photoresist film in a photolithography process or the like in manufacturing of a semiconductor device is widely used not only in the manufacturing of a semiconductor device but also in the field of MEMSs (microelectromechanical systems) and the like.
For example, it is used as an etching mask for three-dimensionally forming a movable portion of a MEMS. In the case of forming a step with respect to a depth direction, use of a photoresist film facilitates processing with favorable accuracy maintained.
In the field of TFTs (Thin Film Transistors), which are thin-film semiconductor devices, a photoresist film is used to control the amount of impurity to be injected that is necessary for a silicon layer or to designate a region into which the impurity is injected in order to form a channel doping structure for shifting operation characteristics in advance in a channel portion of a TFT, or in order to form a GOLD (Gate-drain Overlapped LDD) structure. JP-A-2006-54424 discloses a method in which a TFT having an LDD structure is formed using a mask having a diffraction grating pattern or a mask having a halftone portion. According to this, a resist pattern having a region with a small film thickness is formed at an end portion with respect to a center portion. Then, a conductive film formed on a semiconductor layer is etched to form a gate electrode having a region with a small film thickness at an end portion with respect to a center portion. An impurity is injected into the semiconductor layer, with this gate electrode as a mask.
In the aforementioned MEMS and TFT forming methods, a thin resist portion and a thick resist portion are temporarily placed, and thereafter a process of removing the thin resist portion is performed. After this process, the thick resist portion that has been partially removed in the process will be used as a mask in a subsequent process. Accordingly, in order for the subsequent process to be correctly performed, for example, the thick resist portion that has been partially removed needs to have a predetermined film thickness. However, the amount of the resist to be removed and a developing capability of a developer are difficult to manage with the previous methods, and there is a problem in that the film thickness and the plane shape of the thick resist portion that has been partially removed after the removal of the thin resist portion significantly vary, which may possibly affects the quality.